This invention relates to a golf club in which a club shaft made of a fiber-reinforced resin is connected to a club head in an over-hosel type, and more particularly to a golf club in which longitudinal cracking of a shaft tip portion is prevented due to impacts at the time of hitting.
Generally, the following two methods are known for connecting a fiber-reinforced resin club shaft to a club head. As shown in FIG. 17, a first method is a so-called "inner-hosel type" in which a tip portion 1a of a club shaft 1 is fitted into an insertion hole 7 in such a manner as to penetrate up to a sole 6 from above the upper end of a hosel 5 of a club head 4 as shown in FIG. 18, a second method is a so-called "over-hosel type" in which a protrusion 5a formed on the hosel 5 so as to protrude from it, is fitted into a recess 1b formed inside the tip portion 1a of the club shaft 1.
Generally, a fiber-reinforced resin club shaft consists of a laminate of a plurality of bias layers in which reinforcing fibers are inclined with respect to an axial direction of the shaft and straight layers in which the reinforcing fibers are in parallel with the axial direction of the shaft. In a golf club in which the fiber-reinforced resin club shaft is connected to the club head in the over-hosel type, expanding force from inside act on the shaft tip portion due to impacts at time of hitting, etc, so that longitudinal is likely to occur in the straight layers in the axial direction of the shaft, though such crackling does not occur in the bias layers.
To cope with the problem described above, a proposal has been made in the past which disposes a hoop layer of reinforcing fibers crossing orthogonally the axial direction of the shaft, across the entire length of the shaft. According to this proposal, however, since the hoop layer is disposed across substantially the full length of the shaft, overall rigidity of the shaft increases and there occurs the problem that the shaft lacks elasticity at the time of hitting, the distance of a hit ball decreases and feeling worsens at the time of hitting balls. Since the rigidity of the hoop layer is high, the hoop layer cannot be wound easily in a tubular form during molding of the shaft, decreasing efficiency and hence, productivity.